Insurance relies on having a diverse enough pool to distribute the risk, but health insurance can only do that in one of two ways. Either try to force participation, which either doesn't work (as we've seen...not enough healthy people paying in) or incentivizes more use of benefits (after all, you're paying for it anyway) and increases the pool's risk/cost, or voluntary participation and more competition, in both range of coverage and being able to cobble together pools that offset risk. Participation need only be forced because it is a Ponzi scheme, since it is not sustainable without a stead influx of healthy payers. Insurance is not inherently charitable (paying for others). No one knows when they may need the full benefits they pay for, and the insurance companies trade that peace of mind to hedge against higher utilized policies. But even on the free market, if an insurer cannot entice enough buyers, they cannot sufficiently defray their liabilities.
That's not a Ponzi scheme - that's just ordinary insurance, like it all works everywhere on the planet. Single payer health insurance forces participation, and it does work. So do the kinds of forced participation setups Switzerland and Germany use. Medical care insurance that covers any large proportion of a society is inherently charitable - medical care is needed mostly by the young, old, sick, and injured, but it is paid for by the productively employed. That's the basic reason markets don't function in medical care as a whole.
It's a shame that will NEVER happen here. The health insurance companies have a stranglehold on our health care system. Like a 50 ft indestructible adamantine tapeworm.
Insurance relies upon capturing a premium sufficient to cover the risk, costs, and profit. Premium must be consistent with risk. That's what any insurance relies upon. Spreading the risk lowers the the risk and therefore the required premium. Where have you been looking? You don't have to look far to see successful examples, e.g. Canada, Europe, Asia, etc. There are a number of successful examples. In the US certain types of insurance have been long and successfully mandated, i.e. "forced", by law e.g. car insurance. For more than 70 years car liability insurance has been "forced" onto drivers and owners of cars. So "forced" participation does work. Further, insurance isn't a Ponzi scheme, it's an insurance scheme: a risk sharing scheme. Insurance isn't a charity. The fact that some insured people will receive more financial benefit that others doesn't make insurance a charity. I suggest you look up the meaning of those words. Insurance isn't charity. Additionally, it shouldn't a revelation to a capitalist that if you don't get enough customers to support your business, you are going out of business. That's true of any business, not just the insurance business.